Cultured Pearls from the Gulf of California, Mexico

Abstract

Black pearls have been found in Mexico's Gulf of California since the area was settled more than 2,000 years ago. Attempts at culturing pearls in this area have met with varying success over the past century. Today, a pearl farm in Guaymas is producing commercial quantities of mabe as well as bead-nucleated full-round cultured pearls from the indigenous pearl oyster Pteria sterna. This article provides an overview of the history of natural and cultured pearls from Mexico, describes pearl culturing at the Guaymas farm, and focuses on the properties of bead-nucleated cultured pearls from P. sterna. These cultured pearls have a brown or gray to dark gray bodycolor with various interference colors caused by the stacking of platy aragonite crystals and organic matter. One indication of their natural color (and their Mexican provenance) is a red fluorescence to long-wave UV radiation.

Identification of "Chocolate Pearls" Treated by Ballerina Pearl Co.

“…In addition, there are spectroscopic variations among geographic sources of "black" cultured pearls. For example, the 661-694 nm band, which we observed consistently in our Tahitian cultured pearls, was not reported in Mexican cultured pearls (Kiefert et al, 2004), even though they showed very similar coloration. The presence of these bands provides a good indication for substantial quantities of organic components.…”

“…Various organic components occur between the aragonite platelets, producing a range of pearl colors (e.g., Kiefert et al, 2004;Strack, 2006).…”

“…However, the baselines of all the CCPs we examined always increased in general absorption toward the low-wavelength (high-energy) side of the spectra. Untreated cultured pearls from Mexico and South America may show a similar reaction to long-wave UV as CCPs (Kiefert et al, 2004); however, we may expect quite different reflectance spectra in the UV-Vis-NIR range. In addition, very weak or no absorptions at ~407, 497-500, and 650-694 nm provide good evidence of bleaching treatment.…”

Use of calcein to estimate and validate age in juveniles of the winged pearl oysterPteria sterna

“…Usually, the presence of these substances is detected at 390 to 425 nm, depending on the specific structure in a species (Britton 1990). Although Kiefert et al (2004) reported the presence of porphyrins in P. sterna at 400 to 405 nm, we only observed them with a blue-light filter in the range of 330 to 385 nm, and not at 450 to 480 nm.…”

Age Determination of Pearls: A New Approach for Pearl Testing and Identification

“…Yet, pearl farming remains an interesting craft for local communities, as it has the potential to create a sustainable development in remote coastal areas (Cartier and Ali 2012). Commercially operating pearl farms are now located in the Pacific (French Polynesia, Cook Islands, Fiji, Micronesia), Australia, Indonesia, the Philippines, Vietnam, Thailand, Myanmar, the Arabian Gulf, Sudan (Red Sea), Tanzania, and even in Baja California, Mexico (Kiefert et al 2004;Brown 2005;Southgate et al 2006;Strack 2006;Southgate and Lucas 2008;Müller 2009;). …”